Pseudomonas putida grows with toluene as the sole source of carbon and energy. Crude dell extracts prepared from this organism oxidize toluene through cis-1(S),2(R)-dihydroxy-1,2-dihydrotoluene. The enzyme has been resolved into three protein components. Each protein will be purified, characterized and used in reconstitution experiments to study the mechanism of enzymatic oxygen fixation. Pseudomonas sp. NCIB 9816 grows with naphthalene as the sole source of carbon and energy. Crude cell extracts contain an enzyme that oxidizes naphthalene to cis-1(R),2(S)-dihydroxy-1,2-dihydronaphthalene. This enzyme has been resolved into three proteins whose properties differ from those described above in toluene oxidation. Each protein of the naphthalene dioxygenase system will be purified and used to study the mechanism of enzymatic oxygen fixation.